Respiratory diseases resembling influenza has infected thousands of dogs in the U.S. Recurrent outbreaks of severe respiratory disease characterized by coughing and fever have occurred in greyhounds at racing kennels. Pathological findings included severe pulmonary and plural hemorrhage, accurate to subacute erosive to hyperplastic tracheitis, bronchitis and bronchiolitis and bronchopneumonia. In 2004, eight greyhounds in Jacksonville, Fla. were killed by an equine influenza virus that jumped the species barrier from horses to dogs.
Equine influenza is a disease of horses, and the virus is in the same group of viruses that cause flu in people. The disease is present in horse populations throughout Europe, North America and parts of Asia, with horses typically developing a fever and a dry hacking cough. In the early stages of the disease, horses are reluctant to eat or drink for several days, but usually recover in two to three weeks.
H3N8 subtypes of equine influenza were previously isolated from lungs of two dogs from Florida and one dog from Texas who had died from the infection. Genetic sequence analyses and phylogenetic comparisons determined that all three canine isolates were closely related and evolved from contemporary strains of equine influenza H3N8. Immunohistochemistry demonstrated influenza antigen in bronchial gland epithelial cells, bronchial and bronchiolar epithelial cells and in alveolar macrophages. Seroconversion to canine influenza virus was demonstrated by hemagglutination inhibition and microneutralization assays.
Molecular and antigenic analyses of three influenza viruses isolated from outbreaks of severe respiratory disease in racing greyhounds revealed that they are closely related to H3N8 equine influenza virus (see, e.g., Crawford et al., Science. 2005 Oct. 21;310(5747):482-5. Epub 2005 Sep. 26). Phylogenetic analysis indicated that the canine influenza virus genomes form a monophyletic group, consistent with a single interspecies virus transfer. Molecular changes in the hemagglutinin suggested adaptive evolution in the new host. The etiologic role of this virus in respiratory disease was supported by the temporal association of rising antibody titers with disease and by experimental inoculation studies. The geographic expansion of the infection and its persistence for several years indicate efficient transmission of canine influenza virus among greyhounds. Evidence of infection in pet dogs suggests that this infection may also become enzootic in this population.
In 2005, a mutated form of the Bird Flu (H3N8 Virus) was reported to have killed greyhounds in Massachusetts.
Accordingly, there is a need for an effective vaccine against influenza in canines.
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